In an unprecedented public push to change Amazon policies, nearly 4,500 employees have put their names to a letter asking CEO Jeff Bezos and the commerce giant’s board of directors to become global leaders in fighting climate change.

The letter, posted online Wednesday, is the latest step up in an internal drive by employees for a comprehensive corporate climate strategy. “We have the power to shift entire industries, inspire global action on climate, and lead on the issue of our lifetimes,” the group of employees, calling themselves Amazon Employees for Climate Justice, write.

The group is asking Amazon to set timelines consistent with a scientific consensusthat calls for greenhouse gas emissions to be cut in half by 2030 to avoid ever-greater climate catastrophes, and commensurate with the company’s industry-leading position. But the company’s board of directors says Amazon is already doing, or planning to do, what the employees are asking for.

“Amazon has the resources and scale to spark the world’s imagination and redefine what is possible and necessary to address the climate crisis,” write the employees, who are from some 28 countries and work in warehouses, data centers, engineering hubs, media studios and corporate headquarters. “We believe this is a historic opportunity for Amazon to stand with employees and signal to the world that we’re ready to be a climate leader.”

Amazon, as the avatar of modern consumption-driven capitalism, has become perhaps the biggest target of pressure outside of the fossil-fuels industry for those concerned about climate change. Indeed, it received more activist shareholder proposals on climate and other environmental, social and governance issues this year than any other company, according to the Interfaith Center on Corporate Responsibility. ExxonMobil and Chevron were previously the top targets.

The Amazon employees argue that the company’s guiding principle—obsession with customers—necessitates a fulsome climate response in the face of a global crisis: “In our mission to become ‘Earth’s most customer-centric company,’ we believe our climate impact must be a top consideration in everything we do.”

The climate push began in December when a small group of employees, who are also company shareholders by virtue of stock earned as part of their compensation, proposed a shareholder resolution asking the company to publicly report on its plans for climate-driven disruptions and reducing fossil fuel dependence across the company.

That led to a series of internal meetings with Amazon leaders in which employees asked for support of the resolution.

According to the employees, Amazon’s board of directors did not challenge the proposal, so it will go for a vote of the company’s owners at its annual meeting in May. But the board plans to recommend a vote against the proposal, according to a draft statement provided to proponents of the proposal.

That statement lists dozens of climate-related efforts across Amazon’s sprawling business empire, from renewable-energy purchases to packaging improvements to sustainable building practices at its Seattle headquarters campus. Moreover, Amazon said in February it plans to report its “companywide carbon footprint, along with related goals and programs, later this year.”

While the Amazon employees behind the shareholder proposal applaud those efforts, they say Amazon’s climate-related announcements have typically lacked firm timelines and context, such as the company’s total emissions, or have included wiggle words that make them difficult to evaluate.

They’re keeping up the pressure for a comprehensive plan “within the timeline required by science.”

The scientific consensus in the latest report from the Intergovernmental Panel on Climate Change warns that global greenhouse-gas emissions must be reduced 45 percent below 2010 levels by 2030 and brought to zero by 2050 to preserve a chance of holding global-average temperature increases to 1.5 degrees Celsius—a level of warming that is still expected to cause major, disruptive changes to the Earth’s climate and widespread suffering and loss of life.

The Amazon employees who began the effort created a tool allowing colleagues to read and sign the letter with their names and job titles, said Weston Fribley, a front-end software engineer.

The tally of co-signers grew steadily Wednesday after the letter was published, he said. Amazon has some 650,000 employees worldwide, meaning the co-signers represent less than 1 percent of the company. But it’s still an exceptional number of employees to publicly pressure Amazon for a change.

“People are finding their voice,” Fribley said. “They’re feeling encouraged. … I’m happy to work for a company where all these people are so concerned about it, and care about it so deeply.”

While Amazon has a long and growing list of climate-related initiatives, Fribley and his colleagues say this does not yet amount to a comprehensive climate strategy—at least not one that’s been presented publicly.

Earlier this week, for example, Amazon Web Services (AWS) announced plans to purchase wind energy from projects planned in Ireland, Sweden and California. The company said the new projects, combined with its existing portfolio, are expected to generate about as much electricity as Nashville, Tennessee., uses each year.

The company said that in 2018, some 50 percent of the power consumed by the infrastructure supporting its highly profitable but energy-hungry cloud- computing business came from renewable sources, halfway toward a long-term goal, albeit one with no publicly stated timeline. Likewise, the companywide goal of 100 percent renewable energy has no timeline.

But the employees note in their letter that the same AWS infrastructure is used to help the fossil-fuels industry “accelerate and expand oil and gas extraction.” Amazon’s cloud-computing competitors also have dedicated businesses serving the industry, and the company also hosts data sets and provides credits to environmental researchers.

Amazon in February announced a new program called Shipment Zero, a plan that addresses Amazon’s other core business of shipping purchases to customers. Under that plan, Amazon aims for net zero carbon emissions for half of its shipments by 2030.

Dave Clark, Amazon senior vice president of worldwide operations, said in a February blog post that the company has been preparing “an advanced scientific model to carefully map our carbon footprint to provide our business teams with detailed information helping them identify ways to reduce carbon use in their businesses.”

Underscoring the tension between Amazon’s business imperatives and climate pressures, Clark added, “Customers are always going to want more selection, faster delivery speed, and lower costs. We believe that lower costs include lowering the costs to the environment we all live and work in every day.”

The climate-focused employees poke holes in the Shipment Zero commitment as well, noting that the goal of “net zero” emissions suggests the company would offset its emissions by planting trees or buying carbon credits.

That “allows us to continue to pollute,” the employees write, citing the company’s newly ordered fleet of diesel-powered delivery vans. Carbon offsets, they add, “do nothing to reduce our diesel pollution which disproportionately harms communities of color.”

Moreover, Shipment Zero “does not commit to a decrease in emissions compared to current levels,” the employees write. “Given Amazon’s rate of growth, reaching 50 percent net-zero shipments by 2030 could still be an increase in emissions compared to today.”